Is tillering efficiency a relevant trait in selecting for high yield potential in rice?

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Is tillering efficiency a relevant trait in selecting for high

yield potential in rice?

Estela Pasuquin1_{, Bancha Wiangsamut}1_{, Crisanta Bueno}1_{and Tanguy Lafarge}1, 2 1_{IRRI, DAPO Box 7777, Metro Manila, Philippines,}_www.irri.org_Email_{[email protected]} 2_{CIRAD, TA 70/01, avenue Agropolis, 34398 Montpellier, France Email}_{[email protected]}

Dry season 2005, Muñoz High-yielding elite lines I1: IR72

I3: PSBRc82; High-yielding hybrids H3: SL-8 H9: Bigante New plant type N4: IR72967-12-2-3 Dry season 2004, IRRI I1: IR72 H1: IR71676-90-2-2 H2: IR75217H Water depth • 3 cm } from mid-tillering to • 8 cm PI.

Dry season 2004, IRRI High-yielding elite lines I1: IR72

I2: IR64

Low tiller gene introgressed lines with IR64 or IR72 background LTG1 LTG2 LTG3

Dry season 2003, IRRI I1: IR72

H1: IR75217H H2: IR68284H Age of seedlings:

7, 14 and 21 days Wet season 2004, IRRI

High-yielding hybrids H1 : IR75217H H5 : IR78386H H7 : IR79175H H8 : IR80793H High-yielding inbreds I1 : IR72 I2 : IR64 I9 : IR 77958-7-4-3 (A2502) I10 : IR77958-14-4-7 (A2504) I12 : IR76928-74-3-2-1 (A2568)

References

Dingkuhn M, Schnier HF, De Datta SK, Wijangco E, Dorffling K. 1990a. Diurnal and developmental changes in canopy gas exchange in relation to growth in transplanted and direct-seeded flooded rice. Aust. J. Plant Physiol. 17: 119-134.

Schnier HF, Dingkuhn M, De Datta SK, Mengel K, Wijangco E, Javellana C. 1990. Nitrogen economy and canopy carbon dioxide assimilation of tropical lowland rice. Agron. J. 82: 451-459.

Materials and methods

Improving yield potential in rice implies the characterization of particular crop traits that may be used by breeders in their breeding programs. The rice crop is known to initiate and develop many tillers; a significant part of this may be higher than 50%, do not produce any grain. Recent breeding programs for yield potential have selected genotypes with high tillering efficiency (low tiller mortality) such as new plant types to reduce dry matter loss (Schnier et al 1990) and respiration cost (Dingkuhn et al 1990), but they did not produce the expected high yield in experimental fields. A positive correlation of grain yield with tillering efficiency would also imply a detrimental effect of non-productive tillers. We reviewed here a number of our recent field works to characterize the correlation between grain yield and tillering efficiency across genotypes of the same crop duration grown in similar favorable conditions and across crop managements for the same genotype.

Results

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No positive correlation between grain yield and tillering efficiency, εt, was observed

across high-yielding hybrids and elite lines (Fig. 1) and across elite parental lines and their progenies introgressed with low tiller gene (Fig. 2) grown in similar conditions.

Fig. 1. Effect of εton GY during 2004 WS in IRRI

transplanted at 50 plants m-2 _{(12.5 kg ha}-1_). _{Using low tiller gene introgressed lines}Fig. 2. Effect of εton GY during 2004 DS in IRRI

transplanted at 25 plants m-2_{(6.25 kg ha}-1_).

Conclusion

No positive correlation was observed between grain yield and tillering efficiency across high-yielding genotypes grown in the same favorable conditions and across crop management strategies for the same genotype. In contrast, in cases when the rate or start in tiller emergence was strongly affected by either genetic potential or crop management, then a strong correlation was observed between grain yield and any crop traits that represented early crop vigor.

Tillering efficiency did not appear as a relevant trait to select for high yield potential in rice. Other key traits should be considered such as early crop vigor, expressed here as rapid leaf area production, and possibly dry matter accumulation and carbohydrate remobilization during grain filling, in the case of high-yielding genotypes with early crop vigor. In fact, nonproductive tillers were the smallest of the canopy and may not have then competed significantly for access to light with productive tillers but were still able to intercept light not captured by productive tillers. The impact of nonproductive tillers on grain yield through dry matter remobilization should be quantified in further studies.

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Grain yield was not increased when εtwas increased by change in water depth (Fig. 5)

while not affecting any other trait during plant growth.

Fig. 3. Effect of εton GY during 2005 DS in Muñoz either transplanted at 100 pl m-2 (25 kg ha-1) (TP25),

broadcast at 100 plants m-2_{(25 kg ha}-1_{) (SB25) or broadcast at 200 plants m}-2_{(50 kg ha}-1_{) (SB50).}

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No positive correlation between grain yield and εt was observed across elite

lines and hybrids transplanted at 7, 14 or 21d after sowing (Fig. 4).

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A positive correlation between grain yield and early crop vigor (as LAI here, but also valid with early tiller number and shoot dry matter) was observed when either the rate (Fig. 6) or beginning of (Fig. 7) tiller emergence was strongly different between cases.

Fig. 4. Effect of εton GY during 2003 DS in IRRI transplanted at 7, 14 and 21 DAS at 25 plants m-2.

Fig. 5. Effect of water depth on the number of productive tillers during 2004 DS in IRRI transplanted at 25 plants m-2_{(6.25 kg ha}-1_). H20 depth (cm) Tillering efficiency (εt) (%) Grain yield (t ha-1) 3 67 76 8 6.9 + 0.15 6.6 + 0.12

Fig. 6. Effect of leaf area index (LAI) at early growth stage on grain yield using elite lines and low tiller gene introgressed lines during DS 2004 IRRI.

Fig. 7. Effect of early leaf area development as (LAI) on grain yield during 2003 DS, IRRI. εt = PTil / MaxTil,

where εt is tillering efficiency, PTil is the number of productive tillers per unit soil area at maturity, and MaxTil is the highest number of tillers per unit area observed during plant growth with weekly samplings

•

No positive correlation between grain yield and εtwas observed across elite

lines and hybrids either transplanted or direct-seeded (Fig. 3).

This is presented for I1 and was also valid for H1 and N4.

2 0 0 4 D S IR R I- L T G L e a f a re a in d e x (L A I) 0 .0 0 .1 0 .2 0 .3 0 .4 0 .5 0 .6 G rai n y iel d (t h a -1) 3 4 5 6 7 8 9 1 0 Y = 4 .6 3 + 9 .5 2 x r2 = 0 .9 1 L T 1 L T 3 I2 I1 L T 2 40 45 50 55 60 65 70 G rain y iel d ( t ha -1) 5.0 5.5 6.0 6.5 7.0 7.5 8.0 2003 DS IRRI Tillering efficiency (%) 40 45 50 55 60 65 7040 45 50 55 60 65 70 I1 H1 H2 7 14 21 14 21 7 14 7 21 Tillering efficiency (%) Gr ai n y iel d ( t ha -1) 2003 DS, IRRI I1 H1 H2 30 30 2004 DS IRRI-LTG

Leaf are index (LAI) at 33 DAS

Gr ai n y iel d ( t ha -1) 2004WS IRRI-APA Tillering Efficiency (%) 38 40 42 44 46 48 50 52 54 56 Gr ai n Y ie ld (t ha -1) 4.5 5.0 5.5 6.0 6.5 7.0 H7 H8 H5 I12 I9 I1 H1 I2 2004 WS, IRRI-APA Gr ai n y iel d ( t ha -1) Tillering efficiency (%) 2004DS IRRI-LTG Tiller efficiency (%) 50 55 60 65 70 75 80 85 G rai n yi el d ( t ha -1) 3 4 5 6 7 8 9 10 I1 I2 LT3 LT2 LT1 Tillering efficiency (%) 2004 DS, IRRI-LTG Gr ai n y iel d ( t ha -1) I1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 G rai n y iel d ( t ha -1) 5.5 6.0 6.5 7.0 7.5 8.0 H1

Leaf area index 35 DAS (LAI) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 H2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 y=5.98+1.06x r2=0.98 y=6.70+0.93x r2=0.83 y=6.76+0.58x r2=0.68 2003DS IRRI 21 14 7 ₂₁ 14 7 21 14 7 2003 DS, IRRI

Days after sowing (days)

0 40 80 120 0 10 20 30 40 3 cm water level 8 cm water level Pr oduc ti v e ti ll er s ( no. ) pl an t -1 TP25 30 40 50 60 70 Grain Y ield (t ha -1) 3 4 5 6 7 8 9 10 SB25 Tiller Efficiency (%) 30 40 50 60 70 SB50 30 40 50 60 70 H3 H9 I1 N4 I3 H9 H3 I1 N4 I3 H3 I1 H9 I3 N4 Gr ai n y iel d ( t ha -1) Tillering efficiency (%) 2005 DS, Muñoz TP25 SB25 SB50 30 30